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Tempest Recipes: First things first

February 19, 2012

This is not intended as a course on drum synthesis, but rather some basic principles (from my own personal perspective) that can be applied to the DSI Tempest, or any other decent subtractive synthesizer.

I’ll start with some key concepts which will be expanded later as we step-through the synthesis of different drum types. Understanding these concepts is simple enough, but putting them into practice can take time and careful tweaking, with plentiful moments of initial frustration. Tempest is not a preset machine – it needs to be programmed. Impatient types should stick to samplers.

I do not provide the presets. There are couple of reasons for this. The first is that it’s cheating. The best way to learn is to dive-in, roll your own. I will give some pointers, but you have to fill the gaps.

The second is that I don’t want to disappoint people when I don’t ‘nail’ the sound they’re after. That’s not my job – I have my own exploring to do.

A tip to begin with: Visualization tools help you see the waveform and spectrum of sounds you may want to emulate, or as a guide to home-in on those critical frequencies. For this purpose I highly recommend this free VST signal analyzer. Run the Tempest through it when sound-designing. After a while your ear will improve and you may not need it. But it is really useful at the start.

OK, daylight is burning.

Envelopes:

Envelopes are perhaps most important modulation source in any synthesizer, yet their importance and capabilities are often overlooked.

Envelopes give shape to various sound parameters over time, most importantly volume (amplitude) and pitch. Tempest gives you 5 envelopes per sound – Amp and Cutoff are hardwired, but the other three (Pitch/Aux1/Aux2) can be mapped to specific parameters. It’s a good start for a drum synth!

A drum is invariably hit with something. The energy from a swung stick will provide an short energy impulse on impact before bouncing back from the drum head. There is thus an instant Attack and a short Decay (the lenght of the impulse as it dies away) before the Release which consists of the residual vibrations left over from the strike only milliseconds ago. There is no Sustain in percussion (hence the default envelope mode on Tempest is Attack-Decay).

The stages highlighted above are broadly modeled using the ADSR envelopes that are standard on all reasonably-specced synthesizers.

Note that on Tempest, there is an additional parameter called ‘Peak’. This holds the sound at maximum for a defined period after attack, but before decay, allowing more control over the transient. In other words, it provides beef. Heft, if you will.
The Peak parameter is accessed with the rightmost softknob – over the screen – when on the envelopes page.

A critical step in becoming familiar with a synthesizer is to attach an envelope to a the pitch of a sine wave and tweak the envelope while tapping notes on the midi keyboard. This way you can clearly hear the shape of the envelopes.

For drums, you want nice snappy envelopes with exponential segments. These ‘Bendable’ envelopes allow for more nuanced and natural-sounding drum sounds.

On the Tempest, the envelopes are linear, but the can be ‘bended’ by modulating it’s own shape. See the manual for an nice demonstration. This is an important ability because it’s gives us much better control over the shape of sound components than a fixed linear ‘up-down’ envelope. Real sounds are not like that.

A side note here: The envelopes on the Tempest are fast – very fast. You can hear this by loading a bare 130Hz sine into OSC3. At deafault settings (Amp attack = 0) there is a noticeable click. This is a useful additional element to drum patching, but it can be smoothed out by slightly increasing the Attack of the Amp and other envelopes.

Velocity Mapping:

The most important expression tool on a drumsynth. It’s unlikely that any human will hit the same drum with exactly the same strength each time. There are always small variations in pitch, volume, Amp decay, etc due to this ‘humanisation’. Older drum machines lack these micro-variations between hits and this added to their ‘robotic’ feel.

Luckily for us, on most modern synthesizers, including Tempest, we can vary the sound characteristics by velocity i.e. the strength at which the pads are struck, therefore modelling the human situation.

On the Tempest, use the ModPaths menu to map Velocity to Amplitude, Filter, Pitch for example. The key is to use only a small amount – that is if you wish to have small subtle changes between hits. Or go wild if you want all out chaos. With 8 modulation slots per sound, there is no shortage of options.

There are plenty of other interesting targets for velocity control – it’s up to you but do try mappings to Filter FM and feedback, or use velocity to bring in another oscillator on string hits. Experiment as always.

A note here about Tempests envelopes. In an initialised patch, the AMP envelope is, by default, slightly open already. This means that even the slightest touch of the pad will sound the note. By closing this down to zero, and setting the Envelope velocity amount to 127 (=default, press shift + use the same knob to change), the sound will be under full velocity control. MIDI velocity is scaled to 127 values.

Similarly for the other envelopes – initialized, these have both Envelope amount and Envelope velocity amounts set to zero. You need to set them up separately for each new sound. It makes all the difference.

Oscillators:

The Tempest gives us a hybrid of 2 analogue and 2 digital oscillators per sound/voice. They behave differently. Whilst the digital Oscs are precise by default – they sound the same each hit – the analogue Oscillators are by default free-running. This means that each hit will vary slightly because the analogue waveforms are not starting at zero each time. This is nice for synth patches, but for drums it can make some hits sound weaker than others.

Therefore to get a consistent sound from the analogue oscs, you need to set ‘Wave reset’ to On for each one. If you don’t intend to play the drum at various pitches you can ‘Key follow’ to Off. You’ll notice that choosing this option automatically lowers the pitch.

I have also found that assigning each hit to a separate voice increases the consistency of hits. I’m not sure why this is – something to do with voice allocation perhaps, but each voice should, in principle, sound equally consistent, even when dynamically assigned.

On the other hand, it could be argued that it is little idiosyncrasies like this that give analogue synths much of their ‘character’.

Don’t forget to experiment with the suboscillator and Oscillatior sync!

Filters:

For making bog-standard drums, the filters (Lowpass and Hipass) mostly function to control too-high and too-low frequencies. There are notable exceptions that we”ll look at later 😉

A combination of Lowpass and Highpass filters = Bandpass filter. This gives you decent control over the frequencies taken-up by each sound. Apart from shaving-off the extreme highs with the lowpass, a tiny amount of High pass filter can give a surprising boost to the low end. Try it on a kick-drum.

Unless you are aiming for dubby sounds, it’s good practice to apply enough high-pass to be unnoticeable. Inaudible low frequencies will be removed, reducing ‘muddiness’. Think abut this when designing a kit – you want each sound to ring clear and unhindered, so ideally it should occupy it’s own frequency space.

Remember that the lowpass can switch between 4-pole and 2-pole slopes for a smoother effect.

But filters can be used in more creative ways too. Again, the envelopes are critical here – modulating a closed filter to quickly open and shut again gives a good snap, especially with higher resonance. Filter FM (Audio Mod) is a tasty modulation target particularly for snares and cymbals. Envelope settings are of vital importance.

Keep in mind:

In general, percussive sounds don’t have a defined pitch. But longer bass drums, Toms, and chromatic percussion often do, and are perceived as notes. Therefore you should experiment with tuning your kits. This is much easier to do on the Tempest than a real drumkit – so don’t waste the flexibility. The same kit can take on a drastically different sound and feel when drums are tuned differently against each other. Tempest also allows any drum sound to be played chromatically in 16 Tunings mode, though careful patching is needed for usable results. Later I will look a tuning bass drums and toms so that they fit with the key of your song – your kits will ‘fit’ better in most cases.

Experiment, experiment, experiment. Then experiment some more. Tempest gives you the power of a full analogue synthesizer for each sound you make. No hardware drum machine has ever come close to this flexibility and power.

What next?

A firm grip of the principles above will provide a solid grounding for your patching efforts. Other elements like the LFO and the analogue FX will be explored in more detail when looking at different drum types.